Inside the Medical Tent at the Boston Marathon: A Volunteer's Story

John Andersen has manned the microphone inside the medical tent near the Boston Marathon finish line for the past 15 years. This year, the tent became a makeshift trauma unit after the devastating bombs that ripped through the crowd.

You might imagine a scene of pandemonium. Far from it, says Andersen, who tells PEOPLE how the volunteer EMTs, doctors, nurses and other medical staff immediately sprang into orderly action, literally offering the shirts off their backs to assist victims with severe injuries, even as their own lives were potentially in peril.

"There was no chaos at all," says Andersen, a middle-school science teacher and race volunteer who helped to direct the medical team in the tent toward people in need last week.

"To watch these people react the way they did to help people without hesitation was so phenomenal – putting their hands on wounds, taking off their jacket and putting it on wounds, taking the shirt off their back and putting it on a wound to hold back the bleeding. There was such calm in the way the tent functioned. ... They didn't even need to be told what to do. If I could grab every one of them and hug them, I would do it."

Andersen, who was praised by a doctor in the tent for keeping a sense of calm after the bombings, according to the Boston Globe, says it's remarkable that all the gravely wounded are expected to live.

"Every single person who came into the medical tent is still alive today, and that is such a phenomenal tribute to the people inside the tent," says Andersen. "It still gives me goosebumps and probably will for rest of my life. ... Some people rolled right by me, and I would have bet most of them would have died just by the way they looked. I never saw that before in my life and pray I never will again."

The first injured person he saw was Jeff Bauman, who lost both his legs below the knee but was lauded as a hero for reportedly providing information about the alleged attackers. Bauman was later visited in the hospital by Bradley Cooper.

"He just had nothing below the knees left," Andersen says. "He had two belts that were lifting up the stumps that were holding the blood back, regular belts doctors or other people had given him to use as tourniquets. His face had that whitish-gray look like zombies in a movie, but times a hundred."

"The things that bothered me the most were the lack of color in people's faces, and the sight of the blood," he adds. "When you see someone's bone sticking out of a leg and covered in a brown color you know is blood, or someone goes by and you seeing blood dripping down from the fingers where the hand is supposed to be, those are some of the things that went by me."

Andersen says he outwardly kept his cool even as he feared for his wife, fellow volunteer and ER nurse Laurie Andersen, who was outside the tent during the blasts – she was unharmed – and worried there might still be other blasts.

"I kept saying over and over in the microphone: 'You're all medical professionals. Do what you know how to do,' " Andersen says. "My goal was to protect everybody in the tent and get everyone out alive. We accomplished that goal with a huge amount of stress that there could be another device out there."

The team worked quickly to stabilize patients and get them to ambulances and hospitals as police and bomb-sniffing dogs were moving to evacuate the tent in case of further explosions, explains Andersen.

"It was like a well-oiled machine," he says. "As soon as the doctors and nurses were done, they moved right to the next thing. There was no yelling or screaming. All we heard were the sirens, which sounded like they were coming from all angles. The sirens were wailing, but it was quiet. It was eerie."